1. Field of the Invention
The present invention relates to a method for producing resin particles and resin particles produced by the method.
2. Description of the Prior Art
Toners for use in image formation apparatuses employing an electrophotographic system such as printers, copiers, facsimile machines and the like, and powdered paints are formed using fine particles mainly made of a resin material (hereinafter, referred to as “resin particles”).
As for one example of a method for producing such resin particles, a method disclosed in JP-A No. 2004-070303 is known. In this method, droplets of a dispersion liquid in which a dispersoid containing a resin material is finely dispersed in a dispersion medium are solidified to thereby obtain resin particles.
In this method, a dispersion liquid in which a dispersoid containing a resin material is finely dispersed in a dispersion medium is ejected from nozzles in the form of droplets and then the dispersion medium is removed from the droplets while conveying the droplets in an air flow to obtain resin particles. In this method, since each of the droplets contains a plurality of fine particles derived from the dispersoid, each of the resin particles to be obtained is composed of an agglomerate of such fine particles derived from the dispersoid.
However, in this method, since each of the resin particles is an agglomerate composed of such fine particles derived from the dispersoid as described above, the resin particles are likely to be broken up between the fine particles, namely the resin particles produced in such a manner have low strength. In order to enhance the strength of the resin particles, there may be an approach in which fine particles derived from the dispersoid are made to be fused and bonded with each other at a high temperature. However, even in the case where such an approach is used, it is still difficult to sufficiently enhance the strength of the resin particles. In addition, the resin particles obtained in this manner may not have desired properties due to undesirable degeneration of the resin constituting the resin particles.
Further, in this method, if the droplets of the dispersion liquid are heated at a relatively high temperature in order to remove the dispersion medium quickly from the droplets to obtain the agglomerates, there is a case that fine particles derived from the dispersoid are bonded unnecessarily with each other before being agglomerated. In such a case, it becomes difficult to remove the dispersion medium from the inside of the droplets, which results in a case that the obtained agglomerates have voids and different shapes. As a result, resin particles formed from such agglomerates also have large variations in their diameters and shapes. In a case where such resin particles are used as a toner, there is a possibility of causing defective charge since toner particles cannot be frictionally charged with each other when forming a toner image. Further, there is also a possibility of causing improper transfer of a toner when electrostatically attaching toner particles to a photoconductive drum. Furthermore, if such resin particles are used for a powdered paint, there is a case that coating detect such as a pinhole, flaking and the like occurs in a paint coating depending on coating conditions.